ReplicaSet Implementation

ReplicaSetController implements reconcile.Reconciler. It takes the Namespace and Name for
a ReplicaSet object and makes the state of the cluster match what is specified in the ReplicaSet
at the time Reconcile is called. This typically means using a client.Client to read
the same of multiple objects, and perform create / update / delete as needed.

Implement InjectClient to get a client.Client from the application.Builder

Read the ReplicaSet object using the provided Namespace and Name

List the Pods matching the ReplicaSet selector

Set a Label on the ReplicaSet with the matching Pod count

Because the Controller watches for Pod events, the count will be updated any time
a Pod is created or deleted.